An interferon-gamma release assay test performs well in routine screening for tuberculosis

Area of Science:

• Immunology
• Infectious Diseases
• Clinical Diagnostics

Background:

• Interferon-gamma release assays (IGRAs) are standard for diagnosing latent Mycobacterium tuberculosis infection.
• The T-SPOT.TB test is a widely used IGRA for detecting latent tuberculosis.

Purpose of the Study:

• To evaluate the T-SPOT.TB test's performance in routine clinical practice.
• To analyze the positivity rate, odds of positive results, and factors influencing test outcomes, including season and patient demographics.
• To assess the test's sensitivity in culture-verified tuberculosis cases.

Main Methods:

• Retrospective analysis of T-SPOT.TB test results from 1,809 patients.
• Data included patient age, test indications (anti-TNFα therapy, contact tracing, TB suspicion), and mycobacterial culture results.
• Statistical analysis to determine odds ratios for positive and inconclusive results based on indication, season, and age.

Main Results:

• Conclusive results were obtained for 98.4% of patients.
• Positive T-SPOT.TB results varied by indication: 4.6% for anti-TNFα candidates, 19.3% for contacts, and 24.4% for TB suspects.
• Odds of a positive result were significantly higher for TB suspects (OR 6.83) and contacts (OR 4.93) compared to anti-TNFα candidates.
• Inconclusive results were more frequent in autumn/winter (OR 2.53) and in patients under 6 (OR 3.35) or over 75 (OR 2.66).
• The test demonstrated high sensitivity, correctly identifying 41 out of 43 culture-verified M. tuberculosis infections (one false negative).

Conclusions:

• The T-SPOT.TB test is reliable in routine settings, yielding few inconclusive results.
• Seasonal variations and patient age significantly impact the likelihood of inconclusive test results.
• The T-SPOT.TB test exhibits high sensitivity for detecting culture-verified tuberculosis, though false negatives can occur.